1. Field of the Invention
The present invention relates generally to calorimeters that are configured to evaluate the metabolic rate of an individual based on the individual""s respiration. More particularly, the present invention relates to calorimeters that are configured to measure the oxygen consumption of an individual. The present invention also relates to systems that employ measurements taken by calorimeters of the present invention to subsequently determine the cardiac rate of an individual and to therewith evaluate the metabolic rate of an individual, as well as to methods for determining an individual""s metabolic rate.
2. Background of Related Art
It is well known that for every calorie of energy generated by the body, a fixed amount of oxygen is consumed. Some conventional calorimetry methods include measurement of the amount of oxygen consumed by an individual to indirectly determine the metabolic rate of the individual, which is the amount of energy, in calories, generated and, thus, the number of calories consumed, or xe2x80x9cburnedxe2x80x9d, by the individual over a specific period of time.
Exemplary calorimeters that employ such methods are disclosed in U.S. Pat. No. 4,572,208 to Cutler et al. (hereinafter xe2x80x9cCutlerxe2x80x9d) and U.S. Pat. No. 4,856,531 to Merilxc3xa4inen (hereinafter xe2x80x9cMerilxc3xa4inenxe2x80x9d).
Cutler discloses a calorimeter that may be used to determine the metabolic rate of an individual during normal breathing or during respirator-assisted breathing. The Cutler calorimeter includes a mixing chamber for averaging the gases of several expiratory breaths. The flow of the individual""s expiratory respiration is measured by a flow sensor that communicates with the mixing chamber. The calorimeter also includes a switching mechanism that controls the flow of inspiratory, expiratory, and calibration gas mixtures therethrough. A cooler reduces or eliminates the presence of water vapor in gases flowing through the calorimeter by causing such water vapor to condense and precipitate from the gases. The calorimeter also includes a carbon dioxide sensor and an oxygen sensor. The oxygen sensor of the calorimeter disclosed in Cutler is calibrated by allowing a calibration gas, such as room air, with known quantities of oxygen and carbon dioxide to flow into a reference chamber through a variable restrictor or valve. The carbon dioxide sensor must be separately calibrated, using at least one different calibration gas mixture. Data representative of the amounts of carbon dioxide and oxygen present in the individual""s respiration, as well as data representative of the respiratory flow of the, individual during both inhalation and exhalation, are communicated to a microprocessor, which determines the metabolic rate of the individual. Due to the network of conduits in the Cutler calorimeter, as well as the use of switches and valves therein, a pump is used to draw the calibration or evaluated gas mixtures through and out of the calorimeter.
The calorimeter of Merilxc3xa4inen is configured to measure the metabolic rate of an individual whose respiration is assisted by a respirator. That calorimeter also includes a mixing chamber within which the gases of multiple expiratory breaths may be averaged. As gases exit the mixing chamber, an air flow moving at a known, fixed flow rate carries the gases through the calorimeter to carbon dioxide and oxygen sensors. Carbon dioxide and oxygen measurements obtained with the sensors and the known flow rate are then used to determine the metabolic rate of the individual. Merialxc3xa4inen teaches that the carbon dioxide and oxygen sensors of the calorimeter may be calibrated by use of a syringe to inject into the mixing chamber a calibration gas that differs from room air.
Neither the calorimeter disclosed in Cutler nor the calorimeter disclosed in Merilxc3xa4inen is configured to be used to portably measure the metabolic rate of an individual based on the individual""s heart rate.
Another type of calorimeter, which can be used to evaluate the metabolic rate of an individual during exercise, relies on the premise that metabolic rate of each individual is related to that individual""s cardiac rate.
In many calorimeters of this type, particularly in calorimeters that are incorporated into exercise equipment and in portable calorimeters that are designed to be worn by an individual, attempts have been made to generalize the relationship between metabolic rate and cardiac rate. Such calorimeters typically require an individual to input information such as age, gender, and weight. This information is used, based on a statistical sampling of a large group of individuals of similar age, gender, and weight, to provide a profile of the individual that is relied upon in estimating the individual""s metabolic rate based on cardiac rate measurements. Other factors that may contribute to the metabolic rate of the individual, such as the individual""s height, exercise mechanics, cardiac conditioning, and overall physical health, are often not considered when such calorimeters are used to generate metabolic rate data. As a result, these calorimeters are often very inaccurate, providing metabolic rate measurements that vary by as much as 50% or more from the actual metabolic rate of an individual.
U.S. Pat. No. 6,013,009 to Karkanen (hereinafter xe2x80x9cKarkanenxe2x80x9d) discloses a portable heart rate monitor that estimates the metabolic rate of an individual based on measurements of the individual""s cardiac rate. The portable heart rate monitor of Karkanen relies upon a personal heart rate curve for the individual in estimating the individual""s metabolic rate. In order to generate a personal heart rate curve for an individual, the age and weight of the individual are entered into a microprocessor of the portable heart rate monitor. In addition, data regarding multiple test exercises conducted by the individual, including the type of test exercises conducted by the individual (i.e., running or walking), the speed at which the test exercises were conducted, and the individual""s heart rate for each test exercise, are input into the microprocessor of the portable heart rate monitor. For each test exercise, the rate per pound at which the individual burns calories is calculated using a formula that relies upon a statistical sampling of adults that performed the same general type of exercise. The rate per pound is then multiplied by the input weight to determine the rate at which the individual burns calories during each test exercise. Using calorie burn rate data based on each test exercise, a least squares linear regression algorithm is then used to calculate the personal heart rate curve for the individual. During subsequent exercises, this personal heart rate curve is used to estimate, based on the individual""s heart rate, the rate at which the individual burns calories or the total amount of calories burned by the individual over a specific time duration.
Because the portable heart rate monitor of Karkanen relies upon a statistical sampling of data to estimate the metabolic rate of an individual, that portable heart rate monitor relies upon averaged data obtained from a large population of people who performed a similar type of exercise. The portable heart rate monitor of Karkanen does not account for unique factors of the individual that may contribute to the individual""s metabolic rate.
The inventors are not aware of any portable calorimeters or of any calorimetry systems or methods that employ data representative of an individual""s own metabolic rate, as determined based on measurements of the individual""s respiration, to subsequently ascertain the metabolic rate of the individual.
The present invention includes a calorimeter that is configured to evaluate the metabolic rate of an individual by measuring various aspects of the individual""s respiration. The calorimeter relates one or both of the calculated metabolic rate and the measured aspects of the individual""s respiration to the concurrently measured cardiac rate, or heart rate, of the individual. In addition, the present invention includes a portable calorimeter and a system that employ measurements or calculations from the calorimeter to subsequently evaluate the metabolic rate of the same individual based at least in part upon the individual""s heart rate. The present invention also includes methods for evaluating the metabolic rate of an individual.
The calorimeter of the present invention is configured to receive respiratory gases exhaled by an individual. The calorimeter includes a respiratory flow detection component through which expiratory respiration of the individual passes, a mixing chamber in communication with the respiratory flow detection component, and a respiratory oxygen measurement component in communication with the mixing chamber. In use, the force of an individual""s expiratory respiration drives the exhaled respiratory gases through the flow detection component, the mixing chamber, and the respiratory oxygen measurement component, each of which are positioned along a flow path through the calorimeter.
The calorimeter also includes a calibrator in communication with the respiratory oxygen measurement component. The calibrator includes a room air intake component, which, in operation, forces room air at least into the presence of the respiratory oxygen measurement component. Accordingly, room air, which is assumed to include a molecular oxygen fraction of about 20.93%, is used to calibrate the respiratory oxygen measurement component of the calorimeter at least prior to an individual""s first exhalation into the calorimeter.
The respiratory flow detection component and the respiratory oxygen measurement component communicate with respective detectors, which, in turn, communicate data to a processor or to memory associated with the processor. The respiratory flow and respiratory oxygen measurements are used to determine an indicator of the metabolic rate of the individual, such as the total number of calories burned by the individual over a specific duration of time or the rate at which the individual is burning calories at a specific point in time. This indicator of metabolic rate may be stored as data in memory associated with the processor, along with corresponding data representative of one or more corresponding cardiac rates of the individual which are measured substantially concurrently with measurements taken by the calorimeter.
These metabolic rates, or the respiratory flow and respiratory oxygen data, and corresponding cardiac rate data may be communicated, or transmitted, to memory of a portable cardiac rate monitor, which is also referred to herein as a portable calorimeter for simplicity, to be subsequently used to measure the metabolic rate of the individual. The stored data may subsequently be used by the portable calorimeter to subsequently determine the metabolic rate of the individual, based upon the cardiac rate measured by the portable calorimeter, without requiring use of the calorimeter.